The present invention relates to a non-contact type antenna module for transmitting and receiving information by electromagnetic waves and a double-sided adhesive spacer used therefor, and a method of manufacturing an antenna module.
In recent years, there have been distributed non-contact type information communication means that are used for an RFID (Radio Frequency Identification) system such as Osaifu-Keitai (Mobile Wallet) and an IC card. For a module that is used in such a non-contact type information communication means, electronic parts including an insulating base material, a magnetic material, an antenna coil, and an IC chip are essential. The RFID performs information communication with a reader and a writer by using a magnetic field. Therefore, when a conductive body such as a metal is present around the RFID, the reader or writer, an eddy current occurs at the time of passing of the magnetic field through a metal surface, which generates a counter magnetic field in the direction opposite to a magnetic field for communication, resulting in difficulty in communication. Accordingly, a magnetic material is arranged between the metal surface and an IC tag and the like to prevent the magnetic field from passing through the metal surface.
The magnetic material used in the RFID system is required to have high magnetic permeability to obtain the effect described above. A communication characteristic can be improved as a magnetic material thickness becomes larger. On the other hand, because electronic parts such as an insulating base material, a magnetic material, and an antenna coil, which are necessary for the RFID system, need to be superposed in a layer shape, thinning a total thickness of the module is also required. Further, because the module like this may also be arranged on a curved surface, not only on a flat surface, these electronic parts are also required to have flexibility.
An antenna module that satisfies the requirements described above is found in Japanese Laid-open Patent Publication No. 2006-174223, for example, which discloses an antenna module of with a spiral planar antenna set on an aggregate that has a large number of ferrite chips as a magnetic material overlaid on one sheet base material.
A technique of this structure exhibits considerable effects in that: (1) ferrite, which is easily broken when receiving a shock, is formed as a piece of ferrite sheet (a planar aggregate) made of a large number of chips of the smallest shape capable of bearing the shock, and that; (2) an antenna characteristic is improved by making the planar antenna directly contact the planar aggregate, that is, by employing a structure directly placing the spiral planar antenna on the aggregate.
However, an attempt to actually embody this technique faces the following problems. First, in the process of manufacturing chips, chips are formed from a green sheet of ferrite and then sintered, or chips are cutout from the sintered ferrite. Therefore, irregular sizes and shapes of chips in three-dimensions cannot be achieved. Consequently, when the chips of irregular sizes and shapes are laid out on one sheet base material, upper surface heights of the chips do not become flush with each other (a flat surface without unevenness). Therefore, according to JP 2006-174223, a flat surface is formed by superposing another sheet member on the sintered magnetic material, on which the planar antenna is arranged. That is, a total thickness is increased by a thickness of the added sheet member, which is disadvantageous in view of downsizing the antenna module. Further, in a spiral planar antenna made of one conductive wire, a magnetic flux leaks out from a gap between the spiral planar antenna and the aggregate, and as a result, loss of the antenna characteristic occurs.
Second, in the case of arranging the spiral planar antenna on the aggregate, a gap is provided between adjacent chips of the sintered magnetic material, through which the sheet base material and the planar antenna need to be adhered together by an adhesive medium. That is, according to JP 2006-174223, prior to arranging the planar antenna on the sintered magnetic material, the chips of the sintered magnetic material are laid out on the sheet base material with a gap between and then fixed by adhesion. In order to form a flat surface on which the planar antenna is arranged, a process of superposing another sheet member (an adhesive medium) on the chips is required. As a result, not only is there the problem of inevitable loss of the antenna characteristic due to the gap, there is also a problem that a total thickness of the antenna module increases. Further, the manufacturing process becomes complex.